A watch-case of this type is known, in which the metal retaining ring bears directly on the base secured by a bayonet-fitting in a groove provided in the inner wall of the rim. When the base is removed in order to inspect the movement, to adjust or change the battery of an electronic movement, the retaining ring and consequently the movement are no longer retained and there is a risk of them becoming detached from the case. Moreover, all the vertical dimensions of the retaining ring and bayonet mounting have to be respected very strictly in order to facilitate an assembly without play, which requires high precision machining, which is relatively expensive.